The present invention relates to a process for producing a rubber-based composite material which has good adhesion between a rubber layer and a substrate.
Rubber-metal composite materials have been widely used as, for example, rubber vibration insulators. They need (firm) (rubber-to-metal bonding.)
In view of the foregoing, the present applicant proposed in Japanese Patent Laid-open Nos. 87311/1987 and 246278/1987 a process for producing a rubber composite material which is characterized by coating the substrate with a thin film of cobalt or cobalt alloy by xe2x80x9cdry platingxe2x80x9d, thereby achieving firm bonding between rubber and substrate at the time of vulcanization. In addition, the present applicant disclosed in Japanese Patent Laid-open No. 290342/1989 that the rubber composite material is improved in durability (resistance to wet heat deterioration) if the cobalt is oxidized when the cobalt film is formed or after the cobalt film has been formed.
Moreover, the present applicant proposed in Japanese Patent Laid-open No. 296032/1996 correspoding to the (U.S. Patent application Ser. No. 08/634,792) a method for preparing a rubber composite material comprising the steps of forming a thin film of cobalt oxide on a substrate, forming a rubber composition on the thin film, and vulcanizing the rubber composition, said step of forming a thin film of cobalt oxide comprising sputtering a target of cobalt in the presence of an inert gas and a gas having molecular oxygen with an input power which is at least the transition point at which an input voltage between the target and the substrate abruptly rises when an input power is supplied to the target from a DC supply.
This process yields a rubber-based composite material which exhibits good adhesion under the wet heat condition owing to the cobalt oxide (CoOx) film formed in the oxygen gas stream.
(Further,) a rubber-based composite material (such as rubber vibration insulator) often has its bonding interface exposed, and there is a possibility of the bonding interface coming into direct contact with water. In anticipation of such incidences, the composite material undergoes test for adhesive failure under a wet condition.
The rubber-based composite material having a cobalt oxide film on a metal substrate experiences peeling in the test for adhesive failure as soon as the bonding interface is (expose) to water, although it exhibits good adhesion (with rupture occurring always only in rubber) in the ordinary test for adhesive failure. There has been a demand for solution to this problem.
Therefore, it is an object of the present invention to provide a process for producing a rubber-based composite material which (exhibits good adhesion) even in the case where the bonding interface comes into contact with water.
In order to achieve the above-mentioned object, the present inventors carried out a series of (extensive research) which led to the following finding. That is, a rubber-based composite material which is formed by laminating a layer of rubber compound onto a substrate, with a bonding layer of metal or metal compound interposed between them and subsequently vulcanizing the rubber compound, exhibits firm bonding between the rubber layer and the substrate if the rubber compound is vulcanized, with the composition of the rubber compound and the amount of metal in the bonding layer are controlled such that the rate of vulcanization of the rubber compound coincides with the rate of reaction of the bonding layer, to be more specific, the following equation is established:
xxe2x88x9219xe2x89xa7yxe2x89xa70.2xxe2x88x9212
wherein x is the amount (atom %) of metal in the bonding layer, and y is the slope (kgfxc2x7cm/min) of the vulcanization curve of the rubber compound.
(The process under the above-mentioned condition gives the rubber-based composite material improved adhesion in the wet state and also stable adhesion even in the case where the amount of sulfur (as the vulcanizer) and the amount of vulcanization accelerator fluctuate. This effect is significant in the system with a high vulcanization rate. The present invention is based on this finding.)
The present invention provides a process for producing a rubber-based composite material comprising steps of laminating a rubber compound onto a substrate, with a bonding layer of metal or metal compound interposed therebetween, and subsequently vulcanizing the rubber compound, characterized in that vulcanization is carried out by controlling the composition of the rubber compound and the amount of metal in the bonding layer such that the following equation is established:
xxe2x88x9219xe2x89xa7yxe2x89xa70.2xxe2x88x9212
wherein x is the amount (atom %) of metal in the bonding layer, and y is the slope (kgfxc2x7cm/min) of the vulcanization curve of the rubber compound.